Exhibit 5.1

1625 Sharp Point Drive
Fort Collins, CO 80525
USA
Phone: 970.221.0108
Fax: 970.407.6550

June 24, 2010

Board of Directors
Advanced Energy Industries, Inc.
1625 Sharp Point Drive,
Fort Collins, Colorado 80525

Ladies and Gentlemen:

     I am the Vice President and General Counsel of Advanced Energy Industries, Inc., a Delaware corporation (the “Company”), and am rendering this opinion in connection with the registration statement on Form S-8 (the “Registration Statement”) filed with the Securities and Exchange Commission relating to the proposed public offering of up to 4,000,000 shares of the Company’s common stock, par value $0.001 per share (the “Shares”), under the Company’s 2008 Omnibus Incentive Plan, as amended (the “Plan”). This opinion letter is furnished to you at your request to enable the Company to fulfill the requirements of Item 601(b)(5) of Regulation S-K, 17 C.F.R. § 229.601(b)(5), in connection with the Registration Statement.

     For purposes of this opinion letter, I have examined copies of such agreements, instruments and documents as I have deemed an appropriate basis on which to render the opinions hereinafter expressed. In my examination of the aforesaid documents, I have assumed the genuineness of all signatures, the legal capacity of all natural persons, the accuracy and completeness of all documents submitted to me, the authenticity of all original documents, and the conformity to authentic original documents of all documents submitted to me as copies (including telecopies). As to all matters of fact, I have relied on the representations and statements of fact made in the documents so reviewed, and I have not independently established the facts so relied on. This opinion letter is given, and all statements herein are made, in the context of the foregoing.

     This opinion letter is based as to matters of law solely on the Delaware General Corporation Law, as amended. I express no opinion herein as to any other laws, statutes, ordinances, rules, or regulations. As used herein, the term “ Delaware General Corporation Law, as amended” includes the statutory provisions contained therein, all applicable provisions of the Delaware Constitution and reported judicial decisions interpreting these laws.

     Based upon, subject to and limited by the foregoing, I am of the opinion that following (i) effectiveness of the Registration Statement, (ii) issuance of the Shares in accordance with the terms of the Plan and any agreements issued pursuant thereto, and (iii) receipt by the Company of the consideration for the Shares specified in the resolutions of the Board of Directors or a duly authorized committee thereof, the Shares will be validly issued, fully paid, and nonassessable.

     This opinion letter has been prepared for your use in connection with the Registration Statement and speaks as of the date hereof. I assume no obligation to advise you of any changes in the foregoing subsequent to the delivery of this opinion letter.

     I hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement. In giving this consent, I do not thereby admit that I am an “expert” within the meaning of the Securities Act of 1933, as amended.

Very truly yours,
 

/s/ Thomas O. McGimpsey  

Thomas O. McGimpsey, Esq. 

Vice President and General Counsel